Aftermarket remote starters are never fun to try and sort out after they start to go bad. I would check and make sure that none of it was left behind. I know (from installing a few remote starters) that most of them have a negative output to trigger door locks and unlocks and GM uses posative to trigger their locks. Getting the outputs right requires the use of relay's. Maybe a couple relays got left behind causing your issues. If the remote starter was just cut off these relays, then if the right wire from them contacts ground, it will trigger your locks. I would take a look. Problem is remote starters/hardware can virtually be installed anywhere.